Touch sensing apparatus and mehtod

ABSTRACT

An apparatus and method for sensing touch between a compression mold and a workpiece located in the compression mold including a mold cavity and a mold closure movable relative to the workpiece. The apparatus may include at least one touch sensor pad positionable to signal touch between the mold closure and the workpiece. The touch sensor pad may be in communication with a touch sensor monitor for indicating touch between the workpiece and the mold closure. The touch sensor pad may also be embodied in a touch sensor assembly.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a touch sensor, and more specifically,to enhancing contact or pressure between a mold closure and a workpieceto prevent lateral movement of the workpiece during compression molding.

[0002] Typically, a multilayered workpiece is formed layer by layer,where individual layers can vary by at least 5-10% in thickness. Theworkpiece is then debulked by applying a vacuum and heat to remove gasand pre-densify the workpiece. Finally, the workpiece is placed in asealed bag in a mold and further densified into a final formed workpieceusing only autoclave air pressure. Compression molding a debulkedworkpiece, however, has been found to provide better exterior surfacegeometry than conventional autoclave molding, as well as forcing theworkpiece to a final geometry which is less dependent on material layervariability.

[0003] In a compression molding process, the preformed workpiece isassembled similar to the autoclave process. Instead of autoclave moldingthe workpiece for final densification, however, the debulked workpieceis placed in a compression mold cavity and a mold closure moves intocontact with the workpiece while the mold is also heated according to apre-determined temperature schedule. Final densification of theworkpiece is performed by compressing the workpiece between the moldcavity and the mold closure within the mold.

[0004] Unfortunately, the act of obtaining better exterior surfacegeometry through compression molding may, in some cases, lead to thegeneration of excessive lateral flow of one or more layers of theworkpiece. The excessive lateral flow may tend to form wrinkles in theone or more layers. Such wrinkles create an abnormality in the workpieceand in some cases may lead to a derating of the strength of the finalformed workpiece.

[0005] One cause for the excessive lateral flow is believed to benon-uniform contact between the mold and the workpiece, particularlyupon initial contact of the mold with the workpiece before compressionmolding commences. Another cause is believed to be non-uniform pressureapplied to the workpiece during compression molding. Consequently, it isdesirable to assure that the mold contacts the preformed workpiece ascompletely and uniformly as possible before and during compressionmolding to reduce the likelihood of excessive lateral motion of theworkpiece relative to the mold. For a similar reason, it is desirable toassure that the pressure applied upon the preformed workpiece duringcompression molding is tailored to get a high quality part.

[0006] Accordingly, there is a need in the art for an improved moldclosure.

SUMMARY OF THE INVENTION

[0007] An apparatus and method is disclosed for sensing touch between acompression mold and a workpiece located in the compression moldincluding a mold cavity and a mold closure movable relative to theworkpiece. The apparatus may include at least one touch sensor padpositionable to signal touch between the mold closure and the workpiece.The touch sensor pad may be in communication with a touch sensor monitorfor indicating touch between the workpiece and the mold closure. Thetouch sensor pad may also be embodied in a touch sensor assembly.

DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a diagrammatic exploded cross-sectional side view of amold closure, a workpiece, a mold cavity and a touch sensor, where themold closure is moved into contact with the workpiece;

[0009]FIG. 2 is a non-exploded view of FIG. 1;

[0010]FIG. 3 is a diagrammatic partial plan view along the line 3-3 ofFIG. 2, but including a plurality of touch sensors;

[0011]FIG. 4 is a schematic diagram of a compression mold, a compressionmold control system and a touch sensor monitor;

[0012]FIG. 5 is a diagrammatic cross-sectional side view of a portion ofa contact type touch sensor pad;

[0013]FIG. 6 is a view similar to FIG. 5 but of an alternativeembodiment of this invention;

[0014]FIG. 7 is a diagrammatic cross-sectional side view of a portion ofa strain gauge type of pressure touch sensor pad;

[0015]FIG. 8 is a view similar to FIG. 7 but of an alternativeembodiment of this invention comprising a piezoelectric type of pressuretouch sensor pad;

[0016]FIG. 9 is a view similar to FIG. 7 but of another alternativeembodiment of this invention comprising a capacitive type of pressuretouch sensor pad;

[0017]FIG. 10 is a view similar to FIG. 7 but of yet another alternativeembodiment of this invention comprising a fiber optic type of pressuretouch sensor pad; and

[0018]FIG. 11 is a flow diagram depicting steps for practicing theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] FIGS. 1-3 diagrammatically illustrate an apparatus 10 for sensingtouch between a mold 26, for example, a compression mold, and aworkpiece 40, typically composed of multiple layers of material. Mold 26may comprise any conventional compression molding machine that includesa compression mold closure 30, a compression mold cavity 28 and a moldaperture 70 leading from inside mold cavity 28 to an outsideenvironment. In one embodiment, mold 26 comprises a four-pistonhydraulic type of compression mold machine, for example, a Murdock™compression mold machine.

[0020] Workpiece 40 can be positioned in mold cavity 28, which moldcavity 28 is preferably substantially fixed relative to workpiece 40,and thereby workpiece 40 is movable relative to mold closure 30. Atleast one touch sensor, such as touch sensor pad 12, is positionable tosignal how mold closure 30 touches workpiece 40. The term touch is usedherein to include any force or effect from mold 26 on workpiece 40 orvice versa. Such touch could range from direct physical touch betweenopposing surfaces of each to touch between opposing surfaces of each viaat least one intermediary means. Also, such touch could range from merecontact, as contact is defined herein, to pressure, as pressure isdefined herein, between opposing surfaces of workpiece 40 and mold 26.

[0021] Referring to FIG. 5, preferably touch sensor 12 typicallycomprises at least a contact sensor, such as a contact type touch sensorpad 14. Pad 14 can generate a signal that indicates when compressionmold closures 30 contacts workpiece 40 as mold closure 30 is moved intoposition towards workpiece 40 and mold cavity 28 (FIG. 2). The termcontact is used herein to include any contact between mold closure 30and workpiece 40 ranging from direct physical contact between opposingsurfaces of each to contact between opposing surfaces of each via atleast one intermediary means. Although contact can be indicated at anytime with this invention, it is most useful to know when initial contactis made between mold closure 30 and workpiece 40. For example, the timeof this initial contact can be usefully employed as “time-zero” to begina two step controlled process of (1) closing mold 26 and (2) startingthe mold heating. Each step preferably has its own baseline schedule ofclosure (or preferred force exerted upon workpiece 40) and heatapplications, respectively, from then on through completion of themolding process. Subsequent contacts across the surface of workpiece 40,however, can also be used to modify these baseline schedules during themolding process.

[0022] Referring to FIG. 7, additionally or alternatively, touch sensor12 may comprise a pressure sensor, such as a pressure type touch sensorpad 84. The pressure sensor can provide a signal that indicates asurface pressure between workpiece 40 and compression mold closure 30adjacent sensor 12, for example, local surface pressure. The termpressure is used herein to include any pressure between mold closure 30and workpiece 40 ranging from direct physical pressure between opposingsurfaces of each to pressure between opposing surfaces of each via atleast one intermediary means. Although pressure can be indicated at anytime with this invention, it is most useful to know what the localworkpiece surface pressure is throughout compression molding afterinitial contact between the mold closure and the workpiece.

[0023] Referring to FIG. 3, at least one sensor 12 preferably comprisesa plurality of sensors 12 disposed to signal touch between mold closure30 and workpiece 40 at a plurality of different points across a surface42 of workpiece 40. As desired, each sensor 12 may include a contactsensor or pressure sensor, or both. Further, referring to FIG. 2, it ispreferred that mold closure 30 tilt relative to workpiece 40 to increasea total number of the plurality of different points signaling touchbetween mold closure 30 and workpiece 40. Tilting may be achievedthrough manipulation of mold closure 30 by manual or automatic means.Preferably, tilting is enabled in opposing directions 34 along at leastone diameter of mold 26 and most preferably along multiple diameters ofmold 26.

[0024]FIG. 4 schematically depicts compression mold 26, a compressionmold control system 36 and a touch sensor monitor 38. Each communicatewith one another to operate mold 26 and monitor and interpret how moldclosure 30 is in touch with workpiece 40. For example, manual orautomatic means may be utilized to monitor touch between workpiece 40and mold closure 30 and also to interpret the signal towards controllingmovement of mold closure 30 based on the interpreted signal.

[0025]FIG. 5 diagrammatically illustrates contact type touch sensor pad14, which pad 14 is positionable between mold closure 30 and workpiece40. Contact type touch sensor pad 14 may comprise a touch sensorassembly 16 including a compliant sheet material 18 and contact typetouch sensor pad 14. For example, excellent results are contemplatedwhen contact type touch sensor pad 14 comprises a membrane switch used,for example, in appliance user interfaces. Such a low pressure sensorpad (e.g., preferably <1 psi), gives a positive signal on contact with avery small deflection and can bear very high loads (i.e., while thecontacts are closed). Further, excellent results are contemplated when,for example, compliant sheet 18 comprises a non-conductive deformablemember from the group consisting of resin, thermoplastic resin andsilicone rubber, such as GE Lexan™ polycarbonate, GE Ultrin™polyetherimide or DuPont Kevlar™ resins.

[0026] Still referring to FIG. 5, in touch sensor assembly 16 eachcontact type touch sensor pad 14 (generally indicated by pads 12 in FIG.3) may be connected to a signal run 20 to provide communication from pad14 to outside of mold 26. For example, metal contact type touch sensorpads 14 and metal signal runs (e.g., wires) 20 may be utilized forsignaling contact with a metal mold closure 30. In such a case, at leastone conventional touch sensor monitor, for example, an Ohm meter 72(FIG. 2), may be connected to signal runs 20 outside of mold 26. Thismay include use of a wire connector junction 22 (FIG. 3) or signal runs20 may extend continuously uninterrupted from pads 14 to outside of mold26. In either case, signal runs 20 exit mold interior through moldaperture 70, or the like, including any of several conventional sealstructures such as elastomeric seals or fast cure seals that can bebroken off signal runs 20 when compression molding is completed.

[0027] In particular, when metal mold closure 30 comes in contact withcontact type touch sensor pads 14 (e.g., touch sensor pads 12 of FIG. 2comprising contact type touch sensor pads), pads 14 signal contact atone or more points across surface 42 of workpiece 40. That is, signalruns 20 may be sequentially connected to a low, DC voltage source whoseother terminal would be connected to metal mold closure 30. As moldclosure 30 moves toward workpiece 40, at least one, and then others andpreferably all, contact type touch sensor pad 14 closes the circuit in asimple continuity check arrangement. This information could beinterpreted, by conventional means, to determine which contact typetouch sensor pad(s) 14 contact mold closure 30. This information may inturn thereby provide direction to a manual operator or automatic controlsystem as to how to tilt mold closure 30 to enhance a touch result, forexample, contact, between mold closure 30 and workpiece 40.

[0028]FIG. 6 diagrammatically illustrates an alternative embodiment of acontact type touch sensor pad 76 and touch sensor assembly 16 of thisinvention. In this embodiment the sensor can be completely encapsulatedwithin compliant sheet material 18. Contact type touch sensor pad 76 canbe formed by two opposing surfaces of signal run 20 (for example, awire) spaced from each other by an insulator 24. Such a contact typetouch sensor pad 76 may further include a pair of nubs 56 whereinoutside pressure applied to nubs 56 presses them inward toward eachother and when their opposing surfaces contact, a circuit is completed,including wire run 20. Also, this embodiment need not be compatible withmold closure 30 (i.e., metal to metal, etc.) because contact type touchsensor pad 76 is wholly contained within compliant sheet material 18.Thus, this embodiment may merely depend on signal communication throughcontact type touch sensor pad 76 and signal run 20. Other than thesestructural distinctions, this embodiment is similar to contact typetouch sensor pad 14.

[0029]FIG. 7 diagrammatically illustrates a strain gauge pressure typetouch sensor which is positionable between mold closure 30 and workpiece40. This pressure type touch sensor may also comprise touch sensorassembly 16 including compliant sheet material 18 and a pressure typetouch sensor pad 80 or contact type touch sensor pad(s) 14 or 76, andpreferably both. Such a pressure sensor (e.g., preferably sensitive at10 psi to 1000 psi), more accurately measures local surface pressurebetween workpiece 40 and mold closure 30 throughout compression moldingof workpiece 40. Touch sensor of this invention may comprise a singlestructure having the features and pressure ranges desired for bothcontact type and pressure type touch sensors of the invention.

[0030] Still referring to FIG. 7, for example, excellent results arecontemplated when the pressure type touch sensor comprises a flat straingauge pad 80. Pad 80 may include a resistor 82 mounted on a deflectablebar or disc substrate 84. In use, bending substrate 84 changes theresistance measured by a resistance monitor 86, and this measurement canbe used to determine pressure differentials.

[0031]FIG. 8 diagrammatically illustrates another embodiment of apressure type touch sensor pad 90, which, aside from its particularfunction, is interchangeable with the strain gauge type sensor (FIG. 7).Sensor pad 90 may comprise a piezoelectric sensor pad. The sensor mayinclude electrodes 92 plated on piezoelectric material 94. In use,changes in external pressure change the voltage measured by aconventional voltage monitor 96, and this measurement can be used todetermine pressure differentials.

[0032]FIG. 9 diagrammatically illustrates another embodiment of apressure type touch sensor pad which, aside from its particularfunction, is interchangeable with the strain gauge type sensor (FIG. 7).Sensor pad 100 illustrates a conventional capacitive sensor pad. Thesensor may include deformable material 104 between stiff conductors 102.In use, a gap 106-106 reduces under loading and system capacitanceincreases, as measured by a capacitance monitor 108, and thismeasurement can be used to determine pressure differentials.

[0033]FIG. 10 diagrammatically illustrates another embodiment of apressure type touch sensor pad 110 which, aside from its particularfunction, is interchangeable with the strain gauge type sensor (FIG. 7).Sensor pad 110 illustrates a fiber optic sensor pad. The sensor mayinclude a fiber optic sensor 114, with a phosphor coated tip 120,surrounded by a gel 112 (e.g., silicone rubber) in a pressure-tightelastomeric bag 116. In use, changes in external pressure change the gelpressure on phosphor tip 120 and fluorescent decay time as a function ofpressure is measured by a monitor 118. This measurement can be used todetermine pressure differentials. For example, a Ruxtron Co.™ orPanametrics Co.™ fiber optic pressure type touch sensor pad iscontemplated to produce excellent results.

[0034]FIG. 11 depicts a flow diagram for practicing the invention. Forexample, after a preformed workpiece 40 is debulked and placed in themold cavity 28 opposing the mold closure 30, at least one touch sensor12, and preferably a plurality of contact type and pressure type touchsensors, are positioned adjacent to workpiece 40 or mold closure 30, atstep 44. Next, mold closure 30 and workpiece 40 are moved, preferablyslowly, relative to one another (either or both moving, but preferablyonly mold closure 30 moving) and a signal is generated indicating howmold closure 30 touches workpiece 40, at step 46. As used herein, thesignal may comprise a single signal or multiple signals, either or bothbeing associated with a single touch sensor 12 or multiple touch sensors12 depending on the intended use.

[0035] The step 46 signal is then interpreted to produce an interpretedsignal, by conventional means that may be manual or automatic asdiscussed above, at step 48. Depending on the interpreted signal (e.g.,indicating contact at one or more points across workpiece 40 surface),the movement of mold closure 30 is conventionally guided, manually orautomatically as discussed above, by changing a rate of closure ortilting the same. Preferably, the interpreted signal and guided movementare utilized towards enhancing a touch result between workpiece 40 andmold closure 30, for example, such as increasing the total number of theplurality of different points signaling contact between mold closure 30and workpiece 40, at step 52.

[0036] Alternatively, or additionally, workpiece 40 may then becompression molded, at step 54. Preferably, this may includesubstantially preventing lateral movement of workpiece 40, namely theindividual layers or material thereof, during compression molding. Thismay also include modifying the temperature of workpiece 40, byconventional means, according to a desired temperature schedule asdiscussed previously, at step 74. For example, in addition to enhancingcontact between workpiece 40 and mold closure 30 during compressionmolding, the signal from step 46, or a second signal generated fromtouch sensor 12, may indicate a local surface pressure between workpiece12 and mold closure 30, at step 56, which may also depend on thetemperature of workpiece 40.

[0037] The signal or second signal is then interpreted to produce asecond interpreted signal, by conventional means that may be manual orautomatic as discussed above, at step 58. Depending on the secondinterpreted signal (e.g., indicating contact at one or more pointsacross the workpiece surface indicating what the local pressure is at asurface of workpiece 40), the movement of mold closure 30 is furtherconventionally guided, manually or automatically as discussed above, byfurther changing the rate of closure or tilting the same as donepreviously, at step 60. That is, preferably compression moldingcomprises compression molding workpiece 40 into a high quality part as aresult of the enhanced touch results between workpiece 40 and moldclosure 30, i.e., substantially no wrinkles, substantially full density,substantially no porosity and preferred geometric specifications, atstep 62. In this way, the touch result desired, e.g., maximizing contactbetween workpiece 40 and mold closure 30 or maintaining a desiredpressure at the surface of workpiece 40 in spite of thermal expansionduring molding, can be obtained.

[0038] Yet alternatively, or additionally, the uniform structuralintegrity of the surface of workpiece 40 opposing mold closure 30 ismaintained during the whole process such that any touch upon workpiece40 by touch sensor(s) 12 is negligible to the final formed workpiece, atstep 64. For example, in the embodiment of FIG. 6, this may be achievedby conventional means for maintaining a uniform thickness to the touchsensor assembly 16 in an environment ranging from mere atmosphericpressure to the high pressures experienced during compression molding.In the embodiment of FIG. 5, for example, mold closure 30 may haverecesses (not shown) to receive the contact sensor pads 14 and otherwisemay also maintain a uniform thickness to touch sensor assembly 16similar to the embodiment of FIG. 6.

[0039] After the compression molding step is completed, final formedworkpiece is removed from mold 26, at step 66. Then, preferably, touchsensor(s) 12 or touch sensor assembly 16, is separated from at leastworkpiece 40, at step 68. Alternatively, or additionally, contactsensor(s) 14 may also be separated from mold closure 30. In either case,preferably touch sensor(s) 12, or the touch sensor assembly 16, isreusable from one workpiece to another, and most preferably from onemold 26 to another.

[0040] This invention may have an endless variety of uses for all kindsof compression molded devices. Presently though, excellent results arecontemplated when the invention is used to manufacture aircraft enginefan blades made of laminated sheets of epoxy resin reinforced byunidirectional carbon fiber tows.

[0041] As various possible embodiments may be made in the aboveinvention for use for different purposes and as various changes might bemade in the embodiments above set forth, it is understood that allmatters here set forth or shown in the accompanying drawings are to beinterpreted as illustrative and not in a limiting sense.

[0042] While only certain features of the invention have beenillustrated and described, many modifications and changes will occur tothose skilled in the art. It is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit of the invention.

1. Apparatus for sensing touch between a compression mold and aworkpiece located in said compression mold including a mold cavity and amold closure movable relative to said workpiece, comprising: at leastone touch sensor positionable to signal touch between said mold closureand said workpiece; wherein at least one touch sensor generates a signalthat indicates when said mold closure contacts said workpiece.
 2. Theapparatus of claim 1 , wherein said at least one touch sensor comprisesa plurality of touch sensors disposed to signal touch between said moldclosure and said workpiece at a plurality of different points across asurface of said workpiece.
 3. The apparatus of claim 2 , wherein saidmold closure tilts relative to said workpiece and further comprises acompression mold control system that controls a mold closure rate or atilt of said mold closure based on said signal generated by said atleast one touch sensor.
 4. The apparatus of claim 3 , wherein said atleast one touch sensor further comprises a pressure sensor and in whicha second signal further indicates a surface pressure between saidworkpiece and said mold closure.
 5. The apparatus of claim 1 , whereinsaid at least one touch sensor comprises a touch sensor pad positionablebetween said mold closure and said workpiece.
 6. The apparatus of claim5 , wherein said at least one touch sensor comprises a touch sensorassembly including a compliant sheet and said touch sensor pad.
 7. Theapparatus of claim 6 , wherein said compliant sheet comprises anon-conductive deformable member from said group consisting of resin,thermoplastic resin and silicone rubber.
 8. The apparatus of claim 1 ,wherein said at least one touch sensor is reusable from one workpiece toanother.
 9. A method for sensing touch between a compression mold and aworkpiece located in said compression mold including a mold cavity and amold closure movable relative to said workpiece, comprising: positioningat least one touch sensor to indicate touch between said mold closureand said workpiece; and generating a signal indicating touch betweensaid mold closure and said workpiece, the signal indicating at leastcontact therebetween.
 10. The method of claim 9 , further comprisinginterpreting the signal to produce an interpreted signal for guidingmovement of said mold closure relative to said workpiece.
 11. The methodof claim 10 , in which guiding movement comprises changing a moldclosure rate or a tilt of said mold closure.
 12. The method of claim 10, further comprising enhancing a touch result between said mold closureand said workpiece based on the interpreted signal.
 13. The method ofclaim 12 , in which the touch result comprises contact between said moldclosure and said workpiece.
 14. The method of claim 13 , in which thetouch result further comprises surface pressure between the mold closureand the workpiece.
 15. The method of claim 12 , in which the touchresult comprises surface pressure between said mold closure and saidworkpiece.
 16. The method of claim 12 , further comprising modifying atemperature of said workpiece.
 17. The method of claim 12 , furthercomprising compression molding said workpiece.
 18. The method of claim17 , in which compression molding comprises compression molding saidworkpiece into a high quality part.
 19. The method of claim 18 , inwhich the high quality part is defined by at least one characteristicfrom a group consisting of substantially no wrinkles, substantially fulldensity, substantially no porosity and substantially preferred geometry.20. The method of claim 9 , further comprising maintaining a uniformstructural integrity of a surface of said workpiece opposing said moldclosure.